OEC India Services Interview Questions and Answers

A group discussion (GD) is a structured conversation where a group of people discuss a topic and are observed by a panel of judges or interviewers

Q1. An HR interview is a discussion with a human resources representative to determine if a candidate is a good fit for a company. HR interviewers may ask general questions to gauge a candidate's fit for the c...read more
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Q2. Do you have an HR interview coming up? Along with reviewing your skills and experience, the interviewer will want to assess your self-confidence, interpersonal skills and communication abilities. To make a...read more
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Q1. A one-on-one interview is a job interview where a candidate meets with a single interviewer to discuss their qualifications, experience, and suitability for a role.
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Q2. A one-on-one interview is a job interview where a single candidate meets with a single interviewer to discuss the candidate's qualifications for a job
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Coding tests for interviews are designed to evaluate a candidate's ability to think creatively and adapt their solutions to changing scenarios.

A case study interview is a job interview where a candidate is presented with a business scenario and asked to analyze it and propose a solution.

Interview assessment tests can include aptitude tests, personality tests, cognitive ability tests, presentations, and writing tasks:

Q1. Technical interview questions can cover a range of topics, including your experience, background, and technical skills:
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An aptitude test is quite vital for placements as it helps in enhancing the logical skills of the person and if someone is preparing for interviews then aptitude preparation is very much required.

Q1. Explain the difference between ArrayList and LinkedList in Java. When would you choose one over the other?
Ans. 
ArrayList and LinkedList are both classes in Java that implement the List interface, but they have different underlying data structures.
• ArrayList uses a dynamic array to store elements, providing fast random access but slower insertion and deletion.

• LinkedList uses a doubly linked list to store elements, providing fast insertion and deletion but slower random access.

• Choose ArrayList when you need fast random access and ...read more
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Q2. What are the advantages and disadvantages of using Java’s synchronized keyword for thread synchronization? Can you explain how the ReentrantLock compares to synchronized?
Ans. 
Using synchronized keyword for thread synchronization in Java has advantages like simplicity and disadvantages like potential for deadlock. ReentrantLock offers more flexibility and control.
• Advantages of synchronized keyword: simplicity, built-in support in Java

• Disadvantages of synchronized keyword: potential for deadlock, lack of flexibility

• ReentrantLock offers more control over locking, ability to try and lock with t...read more
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Q3. What is the difference between == and .equals() in Java? When should each be used, and what issues can arise from improper usage?
Ans. 
In Java, == compares memory addresses while .equals() compares values of objects. Improper usage can lead to unexpected results.
• Use == to compare primitive data types or check if two objects reference the same memory address.

• Use .equals() to compare the values of objects, such as strings or custom classes.

• Improper usage of == with objects can lead to unexpected results as it compares memory addresses, not values.
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Q4. How does the Java garbage collector work? Can you describe the different types of garbage collection algorithms available in Java?
Ans. 
The Java garbage collector is responsible for automatically managing memory by reclaiming unused objects.
• The garbage collector in Java runs in the background and automatically reclaims memory from objects that are no longer in use.

• There are different types of garbage collection algorithms in Java, such as Serial, Parallel, CMS, G1, and ZGC.

• Each garbage collection algorithm has its own characteristics and is suitable fo
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Q5. What are the main features of Java 8? Can you explain how lambdas and the Stream API have changed the way Java applications are written?
Ans. 
Java 8 introduced features like lambdas and Stream API which have revolutionized the way Java applications are written.
• Lambdas allow for more concise and readable code by enabling functional programming paradigms.

• Stream API provides a way to process collections of objects in a functional style, making code more expressive and efficient.

• Java 8 also introduced default methods in interfaces, allowing for backward compatib...read more
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Q6. Describe the differences between checked and unchecked exceptions in Java. Provide examples and explain how to handle them properly.
Ans. 
Checked exceptions are checked at compile time, while unchecked exceptions are not. Proper handling involves either catching or declaring the exception.
• Checked exceptions must be either caught or declared in the method signature using the 'throws' keyword.

• Unchecked exceptions do not need to be caught or declared, but can still be handled using try-catch blocks.

• Examples of checked exceptions include IOException and Clas...read more
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Q7. What is the Java Memory Model, and how does it affect multithreading and synchronization? How does volatile help ensure memory visibility?
Ans. 
The Java Memory Model defines how threads interact through memory and how synchronization ensures data consistency.
• Java Memory Model specifies how threads interact with memory, ensuring data consistency

• It defines rules for reading and writing shared variables in a multithreaded environment

• Synchronization mechanisms like synchronized blocks and locks ensure proper visibility and ordering of memory operations

• The 'volatil...read more
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Q8. Can you explain the difference between method overloading and method overriding in Java? Provide examples where each should be used.
Ans. 
Method overloading is when multiple methods have the same name but different parameters, while method overriding is when a subclass provides a specific implementation of a method in its superclass.
• Method overloading is achieved within the same class by having multiple methods with the same name but different parameters.

• Method overriding occurs in a subclass that provides a specific implementation of a method that is al...read more
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Q9. What are functional interfaces in Java? How do they work with lambda expressions? Provide an example of a custom functional interface.
Ans. 
Functional interfaces in Java are interfaces with a single abstract method. They can be used with lambda expressions for functional programming.
• Functional interfaces have only one abstract method, but can have multiple default or static methods.

• Lambda expressions can be used to implement the abstract method of a functional interface concisely.

• An example of a custom functional interface is 'Calculator' with a single abs
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Q10. What is a Java Stream, and how does it differ from an Iterator? Explain how Streams can be used to process collections efficiently.
Ans. 
Java Stream is a sequence of elements that supports functional-style operations. It differs from Iterator by allowing for more concise and declarative code.
• Streams can process elements in a collection in a declarative way, allowing for functional-style operations like map, filter, and reduce.

• Streams do not store elements, they operate on the source data structure (e.g., List) directly.

• Iterators are used to iterate over...read more
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Q11. Explain the concept of immutability in Java. How does the String class achieve immutability, and what are the advantages of immutable objects?
Ans. 
Immutability in Java means objects cannot be modified after creation. String class achieves immutability by not allowing changes to its value.
• Immutability means once an object is created, its state cannot be changed.

• String class achieves immutability by making its value final and not providing any methods to modify it.

• Advantages of immutable objects include thread safety, caching, and easier debugging.

• Example: String s...read more
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Q12. What is the difference between final, finally, and finalize in Java? Provide examples to illustrate their usage.
Ans. 
final, finally, and finalize have different meanings in Java.
• final is a keyword used to declare constants, immutable variables, or prevent method overriding.

• finally is a block used in exception handling to execute code after try-catch block.

• finalize is a method used for cleanup operations before an object is garbage collected.
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Q13. Explain the Singleton design pattern in Java. How can you implement it safely to ensure thread safety?
Ans. 
Singleton design pattern ensures a class has only one instance and provides a global point of access to it.
• Create a private static instance of the class.

• Provide a public static method to access the instance.

• Use synchronized keyword or double-checked locking to ensure thread safety.
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Q14. What are Java annotations, and how are they used in frameworks like Spring? Explain the difference between built-in and custom annotations.
Ans. 
Java annotations are metadata that provide data about a program but do not affect the program itself. They are used in frameworks like Spring to configure and customize behavior.
• Java annotations are used to provide metadata about a program, such as information about classes, methods, or fields.

• In frameworks like Spring, annotations are used to configure various aspects of the application, such as defining beans, handli...read more
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Q15. How do Java Streams handle parallel processing? What are the potential pitfalls of using parallel streams, and how can they be mitigated?
Ans. 
Java Streams handle parallel processing by splitting the data into multiple chunks and processing them concurrently.
• Java Streams use the Fork/Join framework to split the data into chunks and process them in parallel.

• Potential pitfalls include increased overhead due to thread management, potential race conditions, and decreased performance for small datasets.

• Pitfalls can be mitigated by ensuring thread safety, avoiding ...read more
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Q16. Explain the difference between ArrayList and LinkedList in Java. ArrayList is implemented as a dynamic array, while LinkedList is a doubly linked list. ArrayList provides fast random access (O(1) complexi...read more
Ans. 
ArrayList is preferred for frequent retrieval operations, while LinkedList is suitable for frequent insertions/deletions.
• Use ArrayList when you need fast random access and retrieval operations, such as searching for elements in a list.

• Choose LinkedList when you need fast insertions/deletions, especially at the beginning or end of the list.

• Consider memory overhead and performance trade-offs when deciding between ArrayLi...read more
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Q17. What are the advantages and disadvantages of using Java’s synchronized keyword for thread synchronization? The synchronized keyword ensures that only one thread can access a block of code at a time. It pr...read more
Ans. 
ReentrantLock should be used instead of synchronized when more flexibility and control over locking mechanisms is needed.
• Use ReentrantLock when you need to implement custom locking strategies or require advanced features like tryLock() and lockInterruptibly()

• ReentrantLock supports fair locking mechanisms, ensuring that threads acquire the lock in the order they requested it

• ReentrantLock allows for more fine-grained con...read more
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Q18. What is the difference between == and .equals() in Java? == checks for reference equality, meaning it compares memory addresses. equals() checks for value equality, which can be overridden in user-defined...read more
Ans. 
In Java, == checks for reference equality while equals() checks for value equality. Misuse of == can lead to logical errors.
• Override equals() when you want to compare the actual content of objects in user-defined classes.

• Override hashCode() alongside equals() to ensure consistent behavior in hash-based collections.

• Implement Comparable interface and override compareTo() for natural ordering of objects.
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Q19. How does the Java garbage collector work? Garbage collection in Java automatically reclaims memory occupied by unused objects. The JVM has different types of GC algorithms, including Serial, Parallel, CMS...read more
Ans. 
Garbage collection in Java automatically reclaims memory occupied by unused objects using different algorithms and memory regions.
• Force garbage collection in Java using System.gc() or Runtime.getRuntime().gc()

• Not recommended to force garbage collection as it can cause performance issues and disrupt the JVM's optimization

• Example: System.gc();
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Q20. What are the main features of Java 8? Java 8 introduced lambda expressions, enabling functional-style programming. The Stream API allows efficient data processing with map, filter, and reduce operations. ...read more
Ans. 
Lambda expressions in Java 8 improve readability and maintainability by allowing concise and functional-style programming.
• Lambda expressions reduce boilerplate code by providing a more compact syntax for implementing functional interfaces.

• They make code more readable by focusing on the behavior being passed as an argument, rather than the mechanics of how it is implemented.

• Lambda expressions enable developers to write ...read more
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2 medium leetcode questions were asked

Q1. Difference between polymorphism and inheritance
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Q2. Dsa question related to array
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Q1. Explain about project
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Q2. What did you do in you internship
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Q1. Technical question related to Java, Spring boot
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Q1. It was somehow managerial plus technical round.
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Q1. Project related question.
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Q1. Roles and responsibilities
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Q2. Problem based questions
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Q3. Code test & discussions over best practices, best solutions, time and space complexities
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Q1. What data structure is used to implement a priority queue?
Ans. 
Binary heap is used to implement a priority queue.
• Binary heap is a complete binary tree where each node has a value greater than or equal to its children.

• It can be implemented using arrays, where the parent of node at index i is at index (i-1)/2.

• Insertion and deletion operations have time complexity of O(log n) in a binary heap.
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Q2. How many trees will a binary tree have?
Ans. 
A binary tree can have any number of nodes, but the maximum number of trees with n nodes is 2^n.
• A binary tree can have 0 nodes, 1 node, 2 nodes, or any number of nodes.

• The maximum number of binary trees with n nodes is 2^n.

• For example, a binary tree with 3 nodes can have up to 8 different structures.
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Q1. SQL Query to return the second highest marks in a student database
Ans. 
Use a SQL query to find the second highest marks in a student database.
• Use the ORDER BY clause to sort the marks in descending order

• Use the LIMIT clause to limit the result to the second row
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Q2. Program to check if two strings are anagrams
Ans. 
Program to check if two strings are anagrams
• Create a function that takes in two strings as input

• Remove any spaces and convert both strings to lowercase for consistency

• Sort the characters in both strings and compare if they are equal to determine if they are anagrams

• Example: 'listen' and 'silent' are anagrams
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A link was provided for the 15-minute online aptitude test.

90 minutes coding round. There were three problems. One for JavaScript and two for ReactJS

Q1. Mostly ReactJS questions were asked and a few Javascript questions were asked.
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Q1. Again a few react based questions then it was mostly discussion on the past experiences.
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Q1. A general discussion about the notice period, compensation, and information about the company's culture was provided.
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Q1. HR asked about my experience, how I work with current team, whether you worked on KMP already. HR also asked 2-3 technical questions like HashSet manipulation, Android activity lifecycle and hashcode in J...read more
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Normal basic question train and few Logic

Q1. What is Continue?
Ans. 
Continue is a keyword in programming that is used to skip the current iteration of a loop and continue with the next iteration.
• Continue is used in loops like for, while, and do-while to skip the current iteration and move to the next one.

• It is often used to skip certain elements in an array or to avoid executing specific code under certain conditions.

• Example: for(int i=0; i<5; i++) { if(i==2) { continue; } System.out.p
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Q2. Break, if else, while
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